1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device comprising a plurality of stacked semiconductor chips.
2. Description of the Related Art
FIG. 2 shows a semiconductor device disclosed in the unexamined Japanese Patent Publication (KOKAI) No. 10-84076.
As shown in FIG. 2, the semiconductor device comprises a small chip 10, a large chip 20, a wiring board 30 having an inner terminal 33 and an outer terminal 36 connected to the inner terminal 33 via an electric wire 38, and an auxiliary frame 40 having a chip-side terminal 43 and a board-side terminal 46 connected to the chip-side terminal 43 using a connecting member 47. The small chip 10 is disposed on a central portion of the wiring board 30. An electrode pad 13 of the small chip 10 is connected to the inner terminal 33 of the wiring board 30 via a solder ball 14. The auxiliary frame 40 is engaged to the outer part of the small chip 10. An electrode pad 46 of the auxiliary frame 40 is connected to the inner terminal 33 of the wiring board 30 via a solder ball 48. The large chip 20 is superposed on the small chip 10 and the auxiliary frame 40, and an electrode pad 23 of the large chip 20 is connected to the chip-side terminal 43 of the auxiliary frame 40 via a solder ball 24.
According to this semiconductor device, however, the board 30 and the large chip 20 are connected to each other using the auxiliary frame 40, and since it is difficult to fabricate the auxiliary frame 40, the auxiliary frame 40 is expensive. Further, in this semiconductor device, since the connecting force between the chip and the board is great, it is difficult to release a thermal stress between the board and the chip generated based on a difference in coefficient of thermal expansion between the board and the chip, and there is a defect that a reliability of a temperature cycle is low.
In the case of a lamination type semiconductor device in which semiconductor chips 71, 72 and 73 are sequentially stacked on aboard 70 shown in FIG. 3, it is necessary to provide the board 70 with through holes 74. Therefore, there is a defect that the manufacturing cost of the board 70 becomes high.
Thereupon, it is an object of the present invention to provide a new, reliable and inexpensively produced semiconductor device in which the above-described defects of the prior art are overcome, a difference in coefficient of thermal expansion between a board and chip is absorbed.
To achieve the above object, the present invention basically employs the following technique.
That is, the present invention provides a semiconductor device having a substrate on which a plurality of semiconductor chips are stacked, wherein the semiconductor device comprising; a first semiconductor chip mounted on the substrate, a plurality of second semiconductor chips size of which are larger than that of the first semiconductor chip and stacked on the first semiconductor chip with a size-increasing order, a bonding pad formed on the semiconductor chip, a circuit pattern formed on the substrate, a bonding wire for connecting the bonding pad formed on the semiconductor chip and the circuit pattern formed on the substrate, a through hole, formed on the substrate, through which the bonding wire is to be inserted, and further wherein the bonding wire is wired so as to be substantially perpendicularly to a surface of the semiconductor chip.
With this structure, since a thermal stress generated based on a difference in coefficient of thermal expansion between the board and the chip is small, a reliability of the semiconductor chip is enhanced, and the semiconductor chip can be fabricated inexpensively.